1. Field of the Invention
The present invention relates to aromatic polyimide polymers based on an amino-monomer containing two hexafluoro-isopropylidine linking groups or two 1-phenyl-2,2,2-trifluorethane linking groups, and having improved physical, mechanical and chemical properties, and to a method for preparing such polymers.
2. Description of Related Art
Polyimide condensation products of 2,2-bis(4-aminophenyl) hexafluoropropane (hereinafter referred to as
4,4'-6F-Diamine) and aromatic dianhydrides are known in the art and are described in U.S. Pat. No. 3,356,648. These polyimides are produced by first preparing a polyamic acid condensation product of the diamine and dianhydride, such as pyromellitic dianhydride and 4,4'-6 F diamine, in suitable solvent, followed by conversion of the polyamic acid to the polyimide. Imidization is preferably carried out by the application of a solution of the polyamic acid to a substrate, by the evaporation of the solvent and by heating the resultant film to temperatures in the order of 270.degree. to 300.degree. C. for about 2 hours. These polyimides possess excellent heat stability, good electrical properties and high tensile strength.
U.S. Pat. No. 4,592,929 discloses similar polyimides prepared by imidization of the polyamic condensation product of 2,2-bis(3-aminophenyl) hexafluoropropane with
4,4'-hexafluoro isopropylidenebis(phthalic anhydride). These polyimides are disclosed to be particularly suitable as protective coatings for solar cells.
U.S. Pat. No. 4,111,906 to Jones et al. discloses polyimides prepared from 2,2-bis[4-(4aminophenoxy)phenyl] hexafluoropropane, and U.S. Pat. No. 4,477,648 to Jones et al. discloses polyimides prepared from 2,2-bis[(2-halo-4-amino-phenoxy)phenyl] hexafluoropropane.
Copending application U.S. Ser. No. 316,254 filed in the USPTO on Feb. 27, 1989 discloses polyamide-imide polymers based on the polymer condensation product of a mixture of trimellitoyl anhydride chloride and at least one diamine selected from the group consisting of 4,4'-bis [4-(aminophenoxyphenyl) hexafluoroisopropyl] diphenyl ether, 4,4'-bis [2-(4-aminophenyl) hexafluoroisopropyl] diphenyl ether and 4,4'-bis [2-(3-aminophenyl) hexafluoroisopropyl] diphenyl ether.
These amino monomers contain two hexafluoroisopropylidene linking groups and are referred to as 12F-Diamines. The polyamide-imide prepared according to the above mentioned application have outstanding flow properties, good thermal properties and good solubility in aprotic organic solvents.
Polyimides prepared from so called 12-F monomers are disclosed in Applicants copending applications Ser. No. 124,720 and Ser. No. 124,704 filed in the USPTO on Nov. 24, 1987. These polymers may be prepared by forming the polymer condensation product of an aromatic diamine and 4,4'-bis[2-(3,4-dicarboxyphenyl) hexafluoroisopropyl] diphenyl ether dianhydride--Ser. No. 124,720--or condensation of an aromatic dianhydride with 4,4'-bis[2-(amino phenoxyphenyl) hexafluoroisopropyl] diphenyl ether--Ser. No. 124,704--. These polyimides are also characterized as having improved solubility in organic solvents, low dielectric constants, superior thermal and thermoxidative stability and improved processing characteristics.